1. Field of Invention
The invention relates to a security device, for example for use on documents and articles of value such as bank notes and the like to reduce the risk of counterfeiting.
2. Description of Related Art
A common form of security device is an optically variable device, such as a hologram or diffraction grating. These devices are commonly formed as relief structures in a substrate, which is then provided with a reflective coating, for example a continuous or partial metallic layer to enhance the replay of the device. The device is then adhered to the article or document which is to be secured.
With the increased sophistication of counterfeiters, it is important to develop known devices so as to enhance their security.
Some examples of known security devices are described in U.S. Pat. No. 5,815,292, U.S. Pat. No. 5,742,411, U.S. Pat. No. 4,662,653 and EP-A-0395410.